How to Use belongsToMany in Eloquent Relationships

Use belongsToMany in an Eloquent model to define a many-to-many relationship between two models. It requires a pivot table with foreign keys, and you call belongsToMany in both related models to link them.

Syntax

The belongsToMany method defines a many-to-many relationship between two Eloquent models. It accepts the related model class as the first argument and optionally the pivot table name, foreign keys, and other options.

• Related Model: The class name of the model you want to relate.
• Pivot Table: The database table that holds the foreign keys of both models.
• Foreign Keys: The column names in the pivot table that reference each model.

php

public function relatedModels()
{
    return $this->belongsToMany(RelatedModel::class, 'pivot_table', 'foreign_key_on_pivot_for_this_model', 'foreign_key_on_pivot_for_related_model');
}

Example

This example shows how to set up a many-to-many relationship between User and Role models using a pivot table role_user. Each user can have many roles, and each role can belong to many users.

php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    public function roles()
    {
        return $this->belongsToMany(Role::class, 'role_user', 'user_id', 'role_id');
    }
}

class Role extends Model
{
    public function users()
    {
        return $this->belongsToMany(User::class, 'role_user', 'role_id', 'user_id');
    }
}

// Usage example:
$user = User::find(1);
foreach ($user->roles as $role) {
    echo $role->name . "\n";
}

Output

Admin
Editor
Subscriber

Common Pitfalls

Common mistakes when using belongsToMany include:

• Not creating the pivot table with the correct foreign keys.
• Using wrong or missing foreign key names in the method parameters.
• Forgetting to define belongsToMany on both related models.
• Assuming the pivot table has an auto-increment ID; it usually only has the two foreign keys.

Always ensure your pivot table matches Laravel's naming conventions or specify the table and keys explicitly.

php

<?php
// Wrong: Missing pivot table or wrong keys
public function roles()
{
    return $this->belongsToMany(Role::class);
}

// Right: Specify pivot table and keys if not default
public function roles()
{
    return $this->belongsToMany(Role::class, 'role_user', 'user_id', 'role_id');
}

Quick Reference

Parameter	Description	Default Value
Related Model	The class name of the related model	Required
Pivot Table	Name of the pivot table	Alphabetical order of model names, snake_case, plural (e.g., role_user)
Foreign Key (this model)	Foreign key column name for this model in pivot	Singular model name + _id (e.g., user_id)
Foreign Key (related model)	Foreign key column name for related model in pivot	Singular related model name + _id (e.g., role_id)

Key Takeaways

Use belongsToMany to define many-to-many relationships between Eloquent models.

Ensure the pivot table exists with correct foreign key columns matching your models.

Specify pivot table and foreign keys explicitly if they don't follow Laravel's naming conventions.

Define belongsToMany on both related models for full relationship access.

Access related models via dynamic properties like $model->relatedModels.